I looked at that N=1 case study when it first came out. I also listened to a few different nutritionists and other experts discuss nutrition during long term extreme exercise.
The general consensus was that for 30 days or less, diet didn’t have a huge detrimental effect on your over all health, but with extreme exertion, and longer time frames, it did. Also, high level athletes that have dietitians and nutritionists as part of the team, are so closely monitored that the slightest differences in blood, heart rate or urine triggers a dietary or exercise adjustment. Thats not even remotely possible on a thru hike.
Their recommendations were to eat as healthy as possible all the time, but for short stretches do whats needed or convenient in the situation. Long term needs much more planning and effort to stay healthy.
None of this is practiced by most people in the US, and finding someone on trail eating healthy is even more difficult.

